Functional transcranial Doppler sonography of cerebral autoregulation - Basics and clinical applications

Functional transcranial Doppler sonography (fTCD) examines changes in cerebral blood flow velocity (CBFV) caused by varying physiological and pathological influences. The study of cerebral autoregulation to determine the relationship between changes in arterial blood pressure (ABP) and CBFV is one of the most important clinical aspects of fTCD. Various paradigms for fTCD autoregulation tests are established: the phenylephrine method for static autoregulation; the leg-cuff, Valsalva, and carotid compression methods, are examples of dynamic autoregulation tests. In the present contribution we introduce cross-spectrum analysis of spontaneous Mayer waves in ABP and CBFV as a recent method of dynamic autoregulation. In normal subjects autoregulation causes a positive phase shift (Delta phi) by about 60 degrees of CBFV in relation to blood pressure waves due to highpass filtering. Patients with disturbed autoregulation (occlusive cerebrovascular diseases, arteriovenous malformations) show a pathologically reduced or complete lack of Delta phi due to blood-pressure passive CBN changes. This method allows continuous autoregulation monitoring, for example on the stroke unit.